The present disclosure relates to the use of magnetic resonance (MR) spectroscopy for measurement of chemical properties or relative concentrations.
Magnetic resonance spectroscopy and (MRS) and magnetic resonance spectroscopic imaging (MRSI) techniques are known in the field of medical diagnosis and medical diagnostic imaging. The magnetic resonance (MR) modality subjects a subject to a uniform magnetic field subject to perturbation by one or more radiofrequency (RF) pulses. In particular, the uniform magnetic field homogenizes the spins of responsive material within the object such that the spins are effectively aligned. An excitation RF pulse may then be applied to synchronize the spins of the responsive material by directionally “tipping” the spins into a plane transverse to the uniform magnetic field. Upon removal of the excitation RF pulse, the spins realign with the uniform magnetic field and, in the process, emit a resonance signal. Differences in these resonance signals attributable to each nuclear species are detected by the imaging system provide useful information about the chemical species being analyzed using the MRS system.
In particular, when the responsive material (such as a hydrogen (H) or carbon-13 (13C) atom) is a constituent of a molecule, the electron cloud of the molecule affects the magnetic field strength experienced by the responsive material. The variation in the effective magnetic field strength results in a small change to the precession frequency, or spin, of the responsive material. This variation in the precession frequency is manifested as a chemical shift that allows different molecules containing the responsive material to be distinguished from one another. For example, this chemical shift may allow different chemicals within the body to be identified and the concentration of such chemicals to be determined.